thaumasite
Sign in to saveThaumasite is a calcium silicate mineral, containing Si atoms in unusual octahedral configuration, with chemical formula Ca3Si(OH)6(CO3)(SO4)·12H2O, also sometimes more simply written as CaSiO3·CaCO3·CaSO4·15H2O.
Key facts
- Mineral.name
- Thaumasite
- Mineral.category
- Sulfate minerals
- Mineral.boxbgcolor
- c6c3b5
- Mineral.image
- Thaumasite w-prehnite Hydrous basic calcium carbonate sulfate and silicate Fairfax Quarry near Contraville Fairfax County Virginia 1641.jpg
- Mineral.caption
- Thaumasite (white) with prehnite (green) from Fairfax Quarry, Virginia
- Mineral.formula
- Ca3Si(OH)6(CO3)(SO4)·12H2O CaSi(OH)6·CaCO3·CaSO4·12H2O CaSiO3·CaCO3·CaSO4·15H2O
- Mineral.IMAsymbol
- Tma
- Mineral.molweight
- 622.62 g/mol
- Mineral.strunz
- 7.DG.15
- Mineral.system
- Hexagonal
- Mineral.class
- Pyramidal (6) H-M symbol: (6)
- Mineral.symmetry
- P63
- Mineral.unit cell
- a = 11.030(7), c = 10.396(6) [Å]; Z = 2
- Mineral.color
- Colorless, white, pale yellow
- Mineral.habit
- Prismatic, fibrous, massive, radial
- Mineral.cleavage
- Indistinct
- Mineral.fracture
- Subconchoidal
- Mineral.tenacity
- Brittle
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Thaumasite is a calcium silicate mineral, containing Si atoms in unusual octahedral configuration, with chemical formula Ca3Si(OH)6(CO3)(SO4)·12H2O, also sometimes more simply written as CaSiO3·CaCO3·CaSO4·15H2O.
It occurs as colorless to white prismatic hexagonal crystals, typically as acicular radiating groups. It also occurs as fibrous masses. Its Mohs hardness is 3.5 and it has a specific gravity of 1.88 to 1.90. Optically it is uniaxial negative with indices of refraction of nω = 1.507 and nε = 1.468. thumb|left|Group of thaumasite prisms from the Kuruman, Kalahari manganese fields, [[Northern Cape Province, South Africa (size: 4.2 × 3.1 × 1.2 cm)]] It occurs as a hydrothermal alteration mineral in sulfide ore deposits and geothermal alteration of basalt and tuff. It occurs with zeolites, apophyllite, analcime, calcite, gypsum and pyrite.